Oscilloscopes and computer systems incorporating display devices have, for many years, produced signals which are within the display capability of the associated display device. For instance, analog oscilloscopes have produced visual displays on cathode ray tubes (CRT) in a real-time condition wherein input signals are displayed as they occur. Generally, the technology of display tubes and systems has always been sufficiently advanced to always permit the signal to be displayed with a minimum of distortion, and in particular, with a minimum of distortion caused by slew-rate limiting. Slew-rate limiting is a distortion caused by the limiting (maximum) rate over which a particular spot or point may be moved over the surface of the CRT, or in the case of X-Y plotters, the display area. This limitation typically has a value in terms of coordinate distance per unit time, such as ten inches per microsecond. As the technology has advanced, the signals to be displayed have begun to exceed the ability of the visual display unit to accommodate the signal excursion without limitation from the inherent display slew-rate limit. Alternately, the expense of a display having sufficiently high slew-rate capability becomes a significant element of the total system cost. Typical examples of this situation are found in high-speed analog oscilloscopes and computer graphics displays.
Previously, to avoid the problem of slew-rate limitation in systems having a signal displayed in one coordinate axis accordign to a display of time in an orthogonal axis, such as a typical oscilloscope display, the rate of increase of the time axis signal is reduced. However, this causes display image flicker (flicker being caused by the CRT image brightness decaying before a retrace occurs), or an restrictive limit on the information which may be displayed without flicker.